Sound recording system



July 14,1942. w. v. WOLFE 2,289,893

SOUND RECORDING SYSTEM Filed June 26, 1959 I 1 Mar-0R MLLACE V VVOLFE,

Patented July 14, 1942 SOUND RECORDING SYSTEM Wallace V. Wolfe, Beverlyto Radio Corporation of tion of Delaware Hills, Calif., assignorAmerica, a corpora- Application June 26, 1939, Serial No. 281,156 9Claims. (01. 179-1003) This invention relates to sound recording systemsand particularly to a system wherein an improved method of and means forobtaining noise reduction is provided.

In copending application Serial No. 168,173, filed October 9, 1937,there is disclosed a sound recording system capable of producing areverse negative or direct positive sound record which is immediatelyavailable for reproduction with a high degree of fidelity. One of theimportant features of the invention described in this copendingapplication. is the provision of anticipatory noise reduction whereinthe variations in the sound track produced by the average signal currentor the envelope of the signal current are effective at a point on thefilm in advance of the point of application of the modulations.

Ordinarily, in avariable area sound recording system, wherein a shutteror shutters are provided for controlling the unmodulated portion of thesound track, and a vibrating element such as a galvanometer mirror isemployed for signal modulation, the shutters are actuated substantiallysimultaneously with the actuation of the galvanometer. ping of the peaksof the modulations particularly during the sudden application of highamplitude sounds due to the inability of the shutters to clear the trackarea for the modulations. By the use of the reverse negative or directpositive 13 system disclosed in the above-mentioned co pendingapplication, it is possible to direct the light beam being modulated bythe envelope currents at a point on a film in advance of the point ofimpression of the modulations so that the track area is prepared for themodulations.

The direct positive type of system, however, provides, afterdevelopment, a positive record which has been produced without the useof a negative.- Although this direct positive system has manyadvantages, one disadvantage thereof might be that there is no negativefrom which to make additional prints. In this case, if further positivesor prints are desired, it is necessary to print a negative from thedirect positive, from which the additional prints may be made, orrerecord to obtain the necessary negative as described in the copendingapplication referred to above. The present invention provides a methodof and system for first producing a negative I or for directly producinga negative which embodies anticipatory noise reduction and from whichany desired number of prints may be made by printing. 1 I

An object of the invention, therefore, is to im- Such a system maypermit clipprove the present systems of sound recording having noisereduction embodied therein.

Another, object of the invention is to provide A further object of theinvention is to pro duce a negative sound record which may be printed toa positive record having anticipatory noise reduction.

Although the novel features which are believed to be characteristic ofthis invention are pointed out with particularity in the claims appendedherewith, the manner of its organization and the mode of its operationwill be better understoodby referring to the following description readin conjunction with the accompanying drawing forming a part thereof, inwhich Figure 1 is a diagrammatic view of the recording system embodyingthe invention;

Figure 2 is a diagram of the slit mask e1ement of Fig. 1;

Figure 3 is a negative sound record produced with the system of Fig. 1;

Figure 4 is a sound record print made from the negative of Fig. 3; and

Figure 5 is a diagram of an aperture arrangement for producting adifferent form of track from that shown in Figs. 3 and 4.

Referring now to Fig. 1, light from a light source represented by afilament 5 is collected by a lens 6, projected through an aperture mask1 and then to a galvanometer mirror 8 by a lens 9. The beam of reflectedlight pre-shaped by the aperture in mask 1 is projected to a slit maskl0 through a condenserlens H and a prism l2. The mask I0 has a recordingor modulation slit l4 and a noise reduction slit l5 therein (see Figs. 2and 5). Light passing through the slit I4 is projected onto a film I!through lenses I8, while light passing through the slit I5 is .projectedon the film I! through a, deflecting prism 20 and lenses 2|.

A'shutter vane 23, operated by a motor 24, is directly behind the noisereduction slit i 5 to intercept the light passing to the film I'Ithrough the slit l5. The shutter 23 is actuated in accordance with theaverage value or the envelope of the currents being recorded andimpressed on motor 24 as in the usual type of noise reduction system. Itis understood, of course, that the usual type of electrical circuit maybe employed for impressing the signal currents to be recorded 8 inaccordance with the amplitude and frequency of the currents.

To explain the operation of the optical recording system shown in Fig.1, reference is made to Fig. 2, which is a view of the slit mask l takenalong the line 22 of Fig. 1. It is to be understood that the aperture ofmask I produces what is known as a Class A sound track, although thisform of track is not limited to this form of aperture, as described inthe abovementioned copending application. In Fig. 2, the slit mask i0 isshown as a rectangular platehaving the elongated slit M for passinglight in accordance with the amplitude and frequency of the sound wavesbeing recorded, and the longer elongated slit l positioned below slit [4for passing light in accordance with the envelope of the sound wavesbeing recorded. The light beam from the aperture mask or plate I isshown on the plate ill in the unshaded portions of the plate. In otherwords, the only portions of the plate [0 not receiving light are showncrosshatched at 26 and 21.

There is also shown in Fig. 2 two positions of the shutter vane 23, thelower outlines being the no-signal position of the shutter, and the dotand dash outlines 29 showing the full-track modulation position of theshutter. Thus, the shutter vane 23 will take a position between thesetwo limiting positions shown at 23 and 29 in accordance with theamplitude of the signal being impressed on the mirror 8. With theshutter 23 in the no-signal position, light will reach the film I! overthe entire sound track area except at the tip portions 30, whichcoincide with the shaded portions 26 and. 21 at 3| and 32 to produce thezero traces, such as shown in Fig. 3 at c.

As disclosed incopending application Serial No. 168,173, referred toabove, the type of recording system just described will produce what iscalled either a reverse negative or a direct positive Class A soundtrack immediately playable, after normal processing, in a soundreproducing machine. This type of record is shown in Fig. 4. This recordhas anticipatory noise reduction as shown by the distance between pointsa and b, since the light passing the noise reduction slit l5 impinges onthe film l1 (running downwardly) at a point in advance of theimpingement of the light modulations through slit l4 (see Fig. 1),although simultaneously with respect to time. The shutter 23 becomesactive at the point a at the time the modulations begin at point b, andthe sound track area is thus prepared in advance for the modulationsregardless of their amplitude of initial impression.

However, the record produced is a print and it is necessary to make anegative, such as shown in Fig. 3, therefrom to provide additionalduplicate prints.

With the present invention, however, such a sound negative may beobtained directly. This is accomplished by recording with the system ofFigs. 1 and 2 upon an auto-positive film such as is now beingmanufactured by Eastman Kodak Co. and called auto-positive. recordingand normal processing, a negative sound track having anticipatory noisereduction is produced. In thi 'case, as shown in Fig. 3, the zero linetraces c and the modulated portion of the track will 'be opaque and theremainder of the sound track area will be transparent so that it may beused for printing any number of prints having anticipatory noisereduction as shown in Thus, by direct Fig. 4. The auto-positive filmrequires the normal commercial type of development, one type ofdeveloper being Eastman SD42.

It is to be understood, of course, that a special reversal developingprocess may be applied to the usual type of film to produce a negative,but this method is not practical from a commercial standpoint nor doesit result in as satisfactory a product.

Referring now to Fig. 5, this view is similar to Fig. 2, like partsbeing given identical numbers. The light beam in Fig. 5 has a lowerrectangular portion and an upper triangular portion, and its vibrationsare normal to the slits M and I5. This type of beam is obtained by onlychanging the mask 1 to one having the proper apertures, with the resultthat a standard duplex variable area track is produced having anticipa--tory noise reduction, as shown in Figs. 3 and 4. The form of this trackwill appear as shown in Figs. 3 and 4 except that the modulations willbe in phase instead of out of phase as shown. It is also to beunderstood that a unilateral or single edge track may be obtained byusing a mask having a shape corresponding to one-half of the mask ofFig. 5. Thus, the invention is applicable to several types of soundtracks, the attendant advantages above-mentioned being applicable toeach type.

I claim as my invention:

1. A variable area sound wave recording system which includes means .forsimultaneously making on an auto-positive emulsion stock a directnegative record of said sound waves and of the volume ,of said soundwaves, and means adapted to position said volume record adjacent to andin advance of said wave record.

2. A sound wave recording system which includes means for simultaneouslymaking on an auto-positive film a direct negative record of said soundwaves and of the volume of said sound waves, and means adapted toposition said records adjacent to and displaced longitudinally from oneanother, said volume record. being positioned in advance of said waverecord, said direct negative being printable to produce a positiverecord.

3. A sound wave recording system comprising means for making on anauto-positive film a direct negative sound record of said sound waves,and means for simultaneously making on said film a direct negativerecord of the volume of said waves, said record of the volume of saidwaves being displaced longitudinally from the record of saidsound wavesand in advance of said wave record.

4. The sound wave record producing method which includeslight-impressing an auto-positive film in accordance with sound waves tobe recorded to make a record thereof, and light-impressing said film inaccordance with the volume of said sound waves to make a record thereofspaced longitudinally from the record of said soundwaves, said volumerecord preceding said wave record.

5. The sound wave recording method which includes light-impressing anauto-positive film in accordance with said sound waves to make a recordthereof, simultaneously light-impressing said film in accordance withthe volume of said sound waves to make a record thereof spacedlongitudinally from said record of said sound waves, said volume recordpreceding said wave record, and normally developing said film.

6. The method of obtaining a negative sound record comprising exposingan auto-positive film exposure, and processing said exposure to producea negative record.

9. The variable area sound wave recording method which includes exposinga film at one point with light modulated in accordance with theinstantaneous variations of said sound waves,

and at another point in accordance with the average value of thevariation of said sound waves, said average value exposure preceding theinstantaneous modulated exposure longitudinally of said film, andprocessing said film to produce a negative record of said sound waves.

WALLACE v. WOLFE.

